VANCOUVER (CBC) - Spacewalkers Mike Fossum and Ron Garan completed a lengthy excursion from the International Space Station Sunday afternoon, returning safely after six hours and 33 minutes, NASA said.

The most exciting moments were during what the crew have dubbed the "windshield wiper manoeuvre," when the station's 17-metre robotic arm took Garan on a wild ride, 24 metres above the station and 338 kilometres from Earth.

Out at the end of the arm, Garan carried an empty nitrogen gas tank from one side of the station to the other, and then swung back with a full one.

"How's your ride, Ronnie?" Fossum asked.

"Great!" Garan said.

The two astronauts from the shuttle Discovery, which took off for the station on May 31, also installed TV equipment and removed a thermal cover from Japan’s new robotic arm. During the two previous spacewalks they outfitted Japan’s Kibo module and did maintenance jobs.

They were helped by Japanese astronaut Akihiko Hoshide and mission specialist Karen Nyberg with Canadarm2, the station’s main robotic arm, NASA said.

Fossum also collected small samples of dust-like debris and grease detected on a solar wing rotating joint on the space station's left side.

Engineers will analyze the debris to see if the material can help them figure out why a similar joint on the right side of the station was clogged with metal shavings.

That clogged joint on the right side has been used only sparingly since last fall, hampering generation of electricity. The joints enable the space station's solar power arrays to rotate and track the sun.

The left side joint is working normally and engineers are trying to prevent it from developing similar problems.

Earlier in the week, astronauts delivered Japan's $1-billion US Kibo science laboratory, which includes a 10-metre robotic arm.

Discovery is scheduled to undock from the station on Wednesday and land on June 14.

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